Filament



tain inherent characteristics an r amed July 10,1923.

UNITED STATES-- PATENT OFFICE.

BOY Di HALL, OF ORANGE, NEW JERSEY,- ASSIGNOB TO WESTINGHOUSE LAMP COMPANY, A CORPORATION OF PENNSYLVANIA.

Io Drawing.

such constituents that when subjected to a' 18 predetermined heat treating schedule, the crystalline structure thereof may readily be givena characteristic formation. It has been found that the crystalline structure of a metallic filament ives it certhatthese characteristics are dependent upon such factors as the composition of the material comprising the filament, any treatment to which it has been subjected, etc. .The'se characteristics manifest themselves by internal alterations of the filament under the influence of electric currents, and are usually designated by the terms ofisetting, sagging, non-sagging, etc. These roperties may be more or less regulated y controlling the crystalline structure of the filament by the addition of certain ingredients to the tungsten durin the process of forming the tungsten pow er into a rod or ingot preparatory to swa 'ng and drawing.

In accordance with the above facts, my invention contemplates the addition of certain auxiliary ingredients to the tungsten comprising a filamenta body, that will impartto the latter, suc inherent characteristics as to make it highly responsive to a seasoning schedule designed to produce a given crystalline formation. to use for the auxiliary ingredients a certain percentage of some oxygen containing compound, such as thoria or other rare earth metal oxide, alumina, etc. that is non-re ducible in hydro n and substantially nonvolatile, and com ine it with another oxide, such as silica, that becomes more or less volatile at high temperatures. I am aware that it has been common heretofore to use a considerable per cent 'ofthorium oxide I propose" Application filed December 18, 1917. Serial No. 207,888.

combined with tungsten as an offset resisting material and to a certain extent it has the function of controlling the subsequent crystallization of the filament, givin 1t an unusual grain fineness. However, have discovered that when used in the percentages now common, namely from 3-7% by volume, it has a deleterious effect in retarding the formation of large over-lapping crystals which are necessary to revent sagging of the filament, especially if of the coiled type. This retardation of the growth of lar e inter-lacing crystals, .I believe, is direct y traceable to the large percentage of thoria present. It is also true that when extremely. large crystals are formed, other points of the lamps efiiciency are'sacrificed, such as long life, etc. It would, therefore, appear that to produce a filament having a crystalline structure which would give non-sagging properties to the filament, it must be of such a compositionas to be inherently capable of assuming a given structure when treated by a seasoning schedule. I have discovered that this ma be accomplished by the mixture ofa small percentage of a compound, such as thorium oxide or other rare earth metal oxide, aluminum oxide, etc., with a certain per cent of silica. Both the oxides of thorium or aluminum and silicon, are non-reducible in hydrogen and each have somewhat the same effect in retarding grain growth. However, the silica may be volatilized at a high temperature and in this way a considerable portion of it is freed from the tungsten during the formation of the tungsten powder into a filament. .The method emlployed by the applicant infabricating t e tungsten into a filamentary body is the one described in the Coolidge Patent 1,082,933 of December 30, 1913. It would seem that a considerable quantity of these auxiliary materials is required at the start of the forming of the tungsten powder into a rod or in t according to the processes practiced in producing ductile tungsten. This is perha due to the fact that in the early stages t a, tungsten metal is worked at a very high temperature and this effects a more or less rapid volatilization of the silica. It, therefore, appears to be necessary that in order to obtain proper control of the inherent roperties desired to be imparted to the lilament so as to make it susceptible to a predetermined seasoning schedule which will induce the formation'of a given crystalline structure, itis necessary t at a relatively large percentage of c stal growth resisting ingredients or materia be present init1ally.

' It is also a condition that one of these resisting materials be of such a composition that it may be gotten rid of later by volatilize.- tion or the like. The quantity of thoria and silica which I have mixed together and produces excellent, results is from 2% to 7% by volume to 1% by weight) of silica and 1% to .4% by volume (05% to 2% by weight) of thoria. In case it is desired to use alumina -instead of thoria, equally satisfactory results may be obtained by adding"1% to 5% by volume (2% to 1% by weight) of alumina with 2% to 7% by volume (25% to 1% by producingsubstantially pure tungsten.

weight) of silica. The use of this last mixture of auxiliary substances may be preferred since a certain percentage of alumi'num is originally carried by the' tungsten as an impurity and must be gotten rid of during the process of refinement find that when these percentages of the materials mentioned are used, a quality of wire is produced that is very responsive to a heat treating schedule such as disclosed b Harry H. Smith in an application filed bearing a similar percentage by volume to is desired to be stances specified, that is,

the tungsten to which they are added. The same 1s true for the other auxiliary ingredients mentioned, and I wish it understood that s1l1ca is simply one of the substances classifiable as volatile at high temperatures.

In the appended, claims, I- have defined certain substances as being" volatile and non-volatile and I wish it understood that these terms as so used are to be considered with reference t9 the temperatures at which aTrefractory metal, such as tungsten, is worked. The same interpretation given to the volatility at high temperatures of one of the subvolatile at a temperature which is hi h relative to these re ulred for theworkmg of tungsten.

at I claim is m invention is I Afilamentary ody composed-mainly of tungsten or equivalent metal that at candescence tends to sag when utilized as I a conductor of electricity, and containing auxiliary ingredients ca'pableof controlling the crystalline structure to produce-a sub stantially non-sagging filament when subjected to a predetermined heat treatment.

2. A filamentary body composed mainly of tungsten orequivalent metal thatat incan descence tends to sag and offset when utilized as a conductor of electricit and containing auxiliary ingredients whic render the filamentary body inherently susceptible toa heat treating schedule designed o produce a crvstalline formation resistan to sagging and offsetting.

3, A filamentary body composed pri-- marily of tungsten and containing a 'nonmetallic material capable of promoting.

crystal growth resistant to sagging when said body is converted. into a filament and heated to elevated temperatures.

4. A filamentary body. composed pri-,.

marily of tungsten and containing a material capable of exerting an influence to promote the development of large crystals having such size and-contour as to prevent substantial sagging or substantial ofi'setting when converted "into 'a filament and heatedto elevated temperatures.

5. A filamentary body composed oftungsten or equivalent material that tends to sag when utilized as a conductor of electricity and containing ingredients capable of promo ting crystal growth in said body when converted into,a filament and heated toelevated temperatures.

6. A filamentary body composed of tungstie m or equivalent material that tends to s g and'oifset when utilized as a conductor of electricity and containing ingredients "capable of promotin crystal growth re-- sistant to,sagging an offsetting.

7. A filamentary body compo p j maiily of tungsten and containing a, t .1 10

rial which volatilizes mainly at high tem-' peratures and is capable of directing crystal growth.

of tungsten and containing a material which volatilizes inainly at high temperatures and 8. A filamentary body composed primarily,

another material substantially non-volatile at such temperatures, said materials being capable of directing the cystalline growth I ofsaidbody.

9. A filamentary body composed primarily of tungsten and having. intimately mo- 'ciated therewith a non-metallic substance 7 capable of promoting crystal-growth. 10. A filamentary body composed pri- .marily of tungsten andhaving intimately associated therewith a compound or compounds containing silicon and oxygen and capable of; directing crystal growth in said associated therewith a compound or compounds containing silicon andoxygen with a small percentage of a substantially nonvolatile compound and capable of directing crystal growth in said body.

13; A filamentary body composed primarily of tungsten and having intimately associated therewith a compound or compounds containing a substance which volatilizes at high temperatures and one which is substantially non-volatile at such temperatures and capable of directing crystal growth in said bod 14. A filamentary body composed primarily of tungsten and having intimately associated therewith a compound or compounds containing ingredients some of which are'volatile at hightemperatu'res and others non-volatile at such temperatures and capable -of directing crystal growth in said bod y 15.. A filamentary body composed primarily of tungsten to which has been added duringits manufacture from 2% to 7% by volume (25% to 1% by weight) of silica and 1% to 5% by volume (2% to 1% by weight) of alumina.

16. A filamentary body composed primarily of tungsten to which has been added during its manufacture from 2% to 7% by volume (25% to 1% by weight) of silica and .'1% to 4% by volume (05% to 2% by wei ht) of thoria.

1%. The method of producing a filamentary body capable of having imparted thereto upon heat-treatment, a crystalline formation resistant to sagging and offsetting, which comprises intimately mixing tungsten or an equivalent metal and auxiliary ingredients capable of directing the crystalline structure of the tungsten, one of said auxiliar ingredients being -substantially non-v0 atile and another of said ingredients being volatile only at high temperatures, and thereafter forminga filamentary body therefrom in accordance with the method herein set forth.

18. The method of producing a filamentary body capable of having imparted thereto upon heat-treatment, a crystalline formation resistant to sagging and offsetting, wliich comprises intimately mixing powdered tungsten, thoria and a compound or compounds containing silicon and oxygen, and forming a filamentary body therefrom in accordance with the method herein set forth. 1 i

19. The method of producing a filamentary body capable of having imparted thereto upon heat-treatment, a crystalline formation resistant to sagging and offsetting, which comprises mixin tungsten, thoria and silica an thereafter powdered forming a filamentarybod in accordance with the method herein set orth.

In testimony whereof, I have hereunto. 

